1. Field of the Invention
The present invention generally relates to a liquid crystal display device, and more particularly, to a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap to substantially reduce the Mura defect.
2. Description of the Related Art
A liquid crystal display device typically includes a pair of substrates which are maintained in a spaced apart, yet parallel relationship with one another. The space between the substrates is commonly referred to as the cell gap. Interposed between the substrates, within the cell gap, is a liquid crystal material which changes its optical characteristics in response to an applied electrical signal.
A plurality of electrodes are disposed upon the inner surface of the substrates in order to control and apply the desired electrical signals to the liquid crystal material. Some LCD devices will have an electrode arrangement which allows a predetermined set of characters or symbols to be generated, while other LCD devices have a matrix of electrodes that form a display comprised of a great plurality of individually accessible pixel elements, each of which may be selectively activated to form an infinite variety of images.
Due to the electro-optical characteristics inherent the liquid crystal material, it will typically assume one state when no electrical signal is applied and will assume another different state when an electrical signal is applied. For example, some liquid crystal materials will assume a reflective state when no electrical signal is applied, and will assume a transmissive state under the influence of an applied electrical signal. Some new liquid crystal materials provide performance with a variety of different gray levels as well.
In order to assure the proper operation of a liquid crystal display device, it is critical that the cell gap is maintained uniformly and precisely throughout the entire display. Even slight deviations in the cell gap will result in a noticeable and defective appearance in the display (so-called Mura defect). This can readily be seen with a conventional LCD display panel when even slight pressure is applied by a fingertip. In response to the pressure, the cell gap in the affected area will be reduced slightly, resulting a dark spot, degradation of contrast or other undesirable defect in the displayed image.
In a conventional technology, the LCD device, as shown in FIG. 1, includes a TFT substrate 61, a color filter substrate 71 and liquid crystal material sandwiched therebetween. The cell gap is maintained by providing a plurality of spacers 79 between the substrates 61 and 71. The spacers 79, which are of a uniform height, are disposed usually randomly within the cell gap, such as by a spraying technique. This generally results in an uneven distribution of spacers. To ensure that an adequate concentration of spacers to maintain the proper cell gap is disposed in all areas of the display, a superfluity of spacers must be used. In addition, according to such conventional techniques for placement of the spacers, they are placed in both xe2x80x9cinactivexe2x80x9d and xe2x80x9cactivexe2x80x9d areas of the display. The xe2x80x9cactivexe2x80x9d areas are those areas of the liquid crystal material which may be selectively activated because they are located between opposed electrodes disposed upon the substrates. The xe2x80x9cinactivexe2x80x9d areas are those areas of the liquid crystal material that cannot be selectively activated because of the absence of opposed electrodes on the substrates.
Inherently, there are several undesirable deficiencies in the structure and performance of the liquid crystal display panel existing in such conventional spacer techniques. Spacers which are disposed in the active display areas, particularly due to the superfluity of spacers, cause defects, such as the degradation of contrast or the undesirable emission of light around the edges of the spacers therein.
Therefore, European Patent 1030211 A2, incorporated herein by reference, discloses a liquid crystal display, shown in FIG. 2, which can omit the step of scattering spacers and thus avoiding deviations in cell thickness due to the uneven distribution of spacers. This LCD generally includes a TFT (Thin Film Transistor) substrate 30, a CF (Color Filter) substrate 40 and a liquid crystal material layer 49 sealed therebetween. As shown in FIG. 2, the projection patterns 45 formed on the CF substrate 40 have a height of about 4.0 xcexcm to keep the uniform cell gap.
However, the spacer in the both liquid crystal displays of the conventional technology and the above mentioned European patent is deposited on the glass substrate and the color filter layer is disposed between the spacer and the substrate.
Now referring to FIG. 4, it depicts a stress-strain diagram of the post spacer of 20"PHgr" xcexcm deposited directly on a glass substrate at room temperature and with a color filter layer interposed between the post spacer and the glass substrate. It will be appreciated that the spacer deposited directly on the glass substrate is substantially elastic, shown as the curve A, but the spacer deposited on the glass substrate with the color filter layer interposed therebetween is partial elastic, shown as the curve B, in which a permanent strain remains after the load is released. Thus, if a pressure (or stress) loaded on the LCD is big enough to result in the permanent strain, the total height of the spacer with the color filter layer deposited on the glass substrate will be changed. In other words, the cell gap may be uneven and the Mura defect may be generated after the LCD panel is loaded with a substantial pressure.
European Patent 1030211 A2 further discloses another structure of the LCD, as shown in the FIG. 3, wherein a black matrix 52 is formed on the glass substrate 51 on the side of a color filter substrate 50 to coincide with a gate bus lines 33b, a drain bus lines 33a, TFTs and auxiliary capacitance electrodes on a TFT substrate 30. This black matrix 52 is formed of black resin to have a thickness of about 4 xcexcm. The color filters 53 (red, green, and blue) are formed at opening portions of the black matrix 52 with a thickness of 1.5 xcexcm. Then, an opposing electrode 54 formed of ITO (Indium-tin Oxide) is formed on the black matrix 52 and the color filters 53. A projection pattern 55 of about 1.5 xcexcm height is formed on the opposing electrode 54 in a zigzag fashion. In the result, the black matrix 52 together with the projection pattern 55 forms a spacing structure for keeping the uniform cell gap with respect to the other substrate, thereby replacing the conventional spacer. However, the black matrix 52 formed of black resin still fails to prevent a permanent strain remaining after the load is released.
Accordingly, there exist needs for providing a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap to substantially reduce the Mura defect.
It is a primary object of the present invention to provide a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap of the LCD device even though the LCD device is loaded with a pressure or a force.
It is another object of the present invention to provide a liquid crystal display device having a structure in which the spacers maintain the uniform and precise cell gap of the LCD device, thereby substantially reducing the Mura defect.
In order to achieve the objects mentioned hereinabove, the present invention provides a color filter substrate for an LCD device. The color filter substrate comprises a transparent substrate having a substantially flat surface, a black matrix, a plurality of color filters, an electrode, a plurality of spacers, and an alignment film. The black matrix is formed on predetermined regions of the substrate. The plurality of color filters are formed between the regions of the black matrix with overlapping portions on the edge. The electrode is formed over the black matrix and the color filters. The plurality of spacers are formed on the regions of the black matrix without overlapping with color filters, and the alignment film for aligning the liquid crystal molecular is formed over the regions of the black matrix, the color filters, the electrode, and the spacers.
The present invention further provides a method for manufacturing a color filter substrate for an LCD device comprising the steps of: providing a transparent substrate having a substantially flat surface; forming a black matrix on predetermined regions of the substrate; forming a plurality of color filters between the regions of the black matrix with overlapping portions on the edge; forming an electrode over the black matrix and the color filters; forming a plurality of spacers on the regions of the black matrix without overlapping with color filters; and applying an alignment film for aligning the liquid crystal molecular over the regions of the black matrix, the color filters, the electrode, and the spacers.
Accordingly, the spacers according to the present invention are directly deposited on the glass substrate so the LCD device can resile well and the cell gap can be kept uniform after enduring a pressure or a force, thereby substantially reducing the Mura defect. In addition, since the spacers according to the present invention can be correctly positioned on the black matrix, the image displayed on the LCD device is not affected by the spacers.